Marco Rubio joined the 2016 presidential race on April 13, 2015, in Miami, Fla. Find out where the 44-year-old junior senator stands on four of the hottest issues in this campaign: immigration, ISIS, the minimum wage and gay marriage. McClatchyNatalie Fertig/McClatchy

Marco Rubio joined the 2016 presidential race on April 13, 2015, in Miami, Fla. Find out where the 44-year-old junior senator stands on four of the hottest issues in this campaign: immigration, ISIS, the minimum wage and gay marriage. McClatchyNatalie Fertig/McClatchy

The outside political action committee supporting U.S. Sen. Marco Rubio in his presidential campaign raised $16.1 million in the first half of the year, with four big donors making up the bulk of that, according to just-filed campaign finance records.

The filing with the Federal Election Commission covered contributions that came in during the first half of the year to Conservative Solutions PAC, a political organization formed to support Rubio’s campaign for president.

The current filing shows three donations -- $1.5 million, $1.5 million, $2 million – with one each in April, May and June.

Lawrence J. Ellison, chairman and chief technology officer for tech giant Oracle, gave $3 million in two donations, in May and in June. Ellison was recently listed No. 3 on the Forbes 400 magazine list of the richest people in American.

Also giving more than $1 million were Besilu Stables LLC in Miami, at $2.5 million; and Laura Perlmutter of Lake Worth, Florida, at $2 million.

Conservative Solutions spent very little during the first half of the year and thus had nearly all its $16 million in the bank as of June 30.

The group is considered a super PAC – an “independent expenditure-only committee” – that may raise unlimited sums of money to spend supporting or opposing political candidates. While there are restrictions on coordination with or direction from an official campaign, such outside groups effectively extend a candidate’s message and can serve as a repository for big-check donors who have already maxed out their contributions to the main campaign committee.